At what week did you start having regular NSTs?

I'm 31 weeks and I'm still seeing my OB every two weeks, next appt at 33weeks ( I thought by now I would start seeing her every week? )
Also she has not mentioned anything about NSTs. I had symptoms of PTL since 24 weeks and had my steroid shots already. Also my OB stopped measuring my cervix at 27 weeks.
At times I worry that I'm not getting enough monitoring.

When did you start going for NST tests ? Do you think my OB's approach is average in regards to visits and monitoring for twin pregnancy?

I think I started around 32 weeks with weekly NST's and OB appointments. One in the beginning of the week and one in the end. With u/s every 3 weeks. I'm having di/di b/g twins. No high bp, no gd, no ptl. Oh and I've only had my cervical lenght checked 3 times since 30 weeks.

I'm 28 weeks and seeing my OB every two weeks. But I see my MFM every week and get the NST done. I do have GD, so I think they started early. They check my cervix on u/s weekly as well. I have alternating growth checks and fluid checks.